package class06;

import java.util.Date;

/**
 * @author zhangchaoliang
 * create 2022
 */
public class FindFirstIntersectNode {

    public static class Node{
        public int value;
        public Node next;

        public Node(int data){
            this.value = data;
        }
    }

    public static Node getLoopNode(Node head){
        if (head==null||head.next==null||head.next.next==null)
            return null;
        Node slow = head.next;
        Node fast = head.next.next;
        while (slow!= fast){
            if (fast.next==null||fast.next.next==null)
                return null;
            fast = fast.next.next;
            slow = slow.next;
        }
        fast = head;
        while (slow!=fast){
            slow = slow.next;
            fast = fast.next;
        }
        return slow;
    }

    public static Node noLoop(Node head1,Node head2){
        if (head1==null||head2==null){
            return null;
        }
        Node cur1 = head1;
        Node cur2 = head2;
        int n = 0;
        while (cur1.next!=null){
            n++;
            cur1 = cur1.next;
        }
        while (cur2.next!=null){
            n--;
            cur2 = cur2.next;
        }
        if (cur1!=cur2){
            return null;
        }
        cur1 = n>0?head1:head2;
        cur2 = cur1==head1?head2:head1;
        n = Math.abs(n);
        while (n!=0){
            n--;
            cur1 = cur1.next;
        }
        while (cur1!=cur2){
            cur1 = cur1.next;
            cur2 = cur2.next;
        }
        return cur1;
    }

    public static Node bothLoop(Node head1,Node loop1,Node head2,Node loop2){
        Node cur1 = null;
        Node cur2 = null;
        if (loop1==loop2){
            cur1 = head1;
            cur2 = head2;
            int n = 0;
            while (cur1!=loop1){
                n++;
                cur1 = cur1.next;
            }
            while (cur2!=loop2){
                n--;
                cur2=cur2.next;
            }
            cur1 = n > 0?head1:head2;
            cur2 = cur1 ==head1?head2:head1;
            n = Math.abs(n);
            while (n!=0){
                n--;
                cur1 = cur1.next;
            }
            while (cur1!=cur2){
                cur1 = cur1.next;
                cur2=cur2.next;
            }
            return cur1;
        }else {
            cur1 = loop1.next;
            while (cur1!=loop1){
                if (cur1 == loop2)
                    return loop1;
                cur1 = cur1.next;
            }
            return null;
        }
    }

    public static Node getIntersectNode(Node head1,Node head2){
        if (head1==null||head2==null)
            return null;
        Node loop1 = getLoopNode(head1);
        Node loop2 = getLoopNode(head2);
        if (loop1 ==null&&loop2==null)
            return noLoop(head1,head2);
        if (loop1!=null&&loop2!=null)
            return bothLoop(head1,loop1,head2,loop2);
        return null;
    }

    public static void main(String[] args) {
        // 1->2->3->4->5->6->7->null
        Node head1 = new Node(1);
        head1.next = new Node(2);
        head1.next.next = new Node(3);
        head1.next.next.next = new Node(4);
        head1.next.next.next.next = new Node(5);
        head1.next.next.next.next.next = new Node(6);
        head1.next.next.next.next.next.next = new Node(7);

        // 0->9->8->6->7->null
        Node head2 = new Node(0);
        head2.next = new Node(9);
        head2.next.next = new Node(8);
        head2.next.next.next = head1.next.next.next.next.next; // 8->6
        System.out.println(getIntersectNode(head1, head2).value);

        // 1->2->3->4->5->6->7->4...
        head1 = new Node(1);
        head1.next = new Node(2);
        head1.next.next = new Node(3);
        head1.next.next.next = new Node(4);
        head1.next.next.next.next = new Node(5);
        head1.next.next.next.next.next = new Node(6);
        head1.next.next.next.next.next.next = new Node(7);
        head1.next.next.next.next.next.next = head1.next.next.next; // 7->4

        // 0->9->8->2...
        head2 = new Node(0);
        head2.next = new Node(9);
        head2.next.next = new Node(8);
        head2.next.next.next = head1.next; // 8->2
        System.out.println(getIntersectNode(head1, head2).value);

        // 0->9->8->6->4->5->6..
        head2 = new Node(0);
        head2.next = new Node(9);
        head2.next.next = new Node(8);
        head2.next.next.next = head1.next.next.next.next.next; // 8->6
        System.out.println(getIntersectNode(head1, head2).value);

    }
}
